Flutter Firestore NoSuchMethodError：方法“ get”在null上被调用

Question

I have a firestore database. What I want to know is how to check if a certain Document reference exists in this database. The code I have used to work but now it's broken.

Get reference

travelTotalReference =
        Firestore.instance.document('$_id/$_presentDate BalanceTotal');

check if data exists

 travelTotalReference.get().then((dataSnapshot) {
        if (dataSnapshot.exists) {
          setState(() {
            travel = dataSnapshot.data['total'];
          });
        }else{
          setState(() {
            travel = 0;
          });
        }
      });

By the way I know for a fact that this Reference does not exists. I just want to make sure that if it does i can update the travel variable.

The error I get

E/flutter (17184): [ERROR:flutter/shell/common/shell.cc(181)] Dart Error: 
Unhandled exception:
E/flutter (17184): NoSuchMethodError: The method 'get' was called on null.
E/flutter (17184): Receiver: null
E/flutter (17184): Tried calling: get()
E/flutter (17184): #0      Object.noSuchMethod 
(dart:core/runtime/libobject_patch.dart:48:5)

Answer 1

If you call an object that doesn't exist, how can you expect your travelTotalReference to be anything but null.

Since then calling get() on it return an error, seems fair...